使用变量，在 switch 语句中初始化，在外部

发布于 2024-12-18 18:32:22 字数 1560 浏览 2 评论 0原文

我在访问 switch 语句中初始化的变量，然后在 switch 外部使用它们时遇到问题。

这就是我的代码应该产生的结果：什么是：X（+-* 或 /）X

这是我的 Java 代码：

import java.util.Random;
import java.util.Scanner;

public class Test2 {
        public static void main(String[]args){

        Random rand = new Random();
        Scanner sc = new Scanner(System.in);

        int svar, ans;
        int tal1 = rand.nextInt(100) + 1;
        int tal2 = rand.nextInt(100) + 1;

        String characters = "+-*/";
        int r = rand.nextInt(characters.length());
        char randomChar = characters.charAt(r);

        switch(randomChar){
        case '+':
            ans = tal1 + tal2;
            break;
        case '-':
            ans = tal1 - tal2;
            break;
        case '*':
            ans = tal1 * tal2;
            break;
        case '/':
            ans = tal1 / tal2;
            break;
        }

        System.out.println("What is: "+tal1+randomChar+tal2+"?");
        svar = sc.nextInt();

        if (svar == ans)
            System.out.println("Correct!");
        else
            System.out.println("Wrong - Right answer: "+ans);

        }
}

如您所见，“ans”已被声明并初始化。但是，我想在 if 语句（为了比较结果）和输出中使用 ans 变量。

现在我可以扩展每个案例并编写 if 语句和输出，但是代码会太多，因为我正在尝试执行类似的代码，但更小。这项工作如何运作有什么建议吗？

这是我得到的编译错误：

Exception in thread "main" java.lang.Error: Unresolved compilation problems: 
    The local variable ans may not have been initialized
    The local variable ans may not have been initialized

    at Test2.main(Test2.java:36)

原文

I have an issue with accessing variables initialized in a switch-statement, and then using them outside switch.

This is what my code should produce:
What is: X (+-* or /) X

Here's my Java code:

import java.util.Random;
import java.util.Scanner;

public class Test2 {
        public static void main(String[]args){

        Random rand = new Random();
        Scanner sc = new Scanner(System.in);

        int svar, ans;
        int tal1 = rand.nextInt(100) + 1;
        int tal2 = rand.nextInt(100) + 1;

        String characters = "+-*/";
        int r = rand.nextInt(characters.length());
        char randomChar = characters.charAt(r);

        switch(randomChar){
        case '+':
            ans = tal1 + tal2;
            break;
        case '-':
            ans = tal1 - tal2;
            break;
        case '*':
            ans = tal1 * tal2;
            break;
        case '/':
            ans = tal1 / tal2;
            break;
        }

        System.out.println("What is: "+tal1+randomChar+tal2+"?");
        svar = sc.nextInt();

        if (svar == ans)
            System.out.println("Correct!");
        else
            System.out.println("Wrong - Right answer: "+ans);

        }
}

As you can see, "ans" has been declared and initialized. However, I want to utilize the ans variable in both the if statement (in order to compare the result) and the output.

Now I could expand each case and write both the if statements and the outputs, but the code would be too exessive as I'm trying to do a similar code, but smaller. Any tips how this work would work?

Here's the compilation error I get:

Exception in thread "main" java.lang.Error: Unresolved compilation problems: 
    The local variable ans may not have been initialized
    The local variable ans may not have been initialized

    at Test2.main(Test2.java:36)

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当梦初醒 2024-12-25 18:32:22

添加 default 大小写以捕获任何无法识别的输入。在您的情况下，这可能会引发 RuntimeException，因为如果达到这种情况，您的代码就会出现问题。

default: 
  throw new RuntimeException("Unexpected operation: " + randomChar);

您收到的错误意味着存在无法初始化 ans 的代码路径。不要采取简单的方法，在声明时使用无意义的值初始化 ans！这只会隐藏有关代码实际问题的宝贵警告。

Add a default case to catch any input that isn't recognized. In your case, this could throw a RuntimeException, since something is wrong with your code if this case is reached.

default: 
  throw new RuntimeException("Unexpected operation: " + randomChar);

The error you are getting means that there is a code path that fails to initialize ans. Do not take the easy way out and initialize ans with a meaningless value when it is declared! That will just hide this valuable warning about a real problem with your code.

回复收藏 0 原文

提笔书几行 2024-12-25 18:32:22

与实例变量不同，局部变量不会自动初始化。

您需要显式地将其初始化为默认值。

 int svar, ans = 0; // assuming 0 is default value for ans

如果您的 switch 中所有情况都失败，则 ans 将永远不会被初始化。

Unlike instance variables, local variables are not automatically initialized.

You need to explicitly initialize it the default value.

 int svar, ans = 0; // assuming 0 is default value for ans

If all the cases fail in your switch then ans will never be initialized.

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梦境 2024-12-25 18:32:22

诸如 ans 之类的局部变量必须在使用前进行初始化。

因此只需将 0 分配给 ans

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等待圉鍢 2024-12-25 18:32:22

如果你声明一个局部变量（在函数内部），你应该总是初始化它，

int svar = 0;
int ans = 0;

如果你在函数外部声明它，那么它将自动初始化为 0，但这对于这个来说不是一个好的做法

If you declare a local var (inside a function) you should always initialize it

int svar = 0;
int ans = 0;

if you declare it outside of a function then it will be automatically initialized with 0, but that's not good practice for this one

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这个俗人 2024-12-25 18:32:22

你会得到这个编译错误，因为编译器不知道 ans 是否会被初始化，
原因是在编译时不知道是否会执行 switch 条件，因此会出现编译错误。要解决此问题，请将 ans 初始化为某个值，例如：

ans = -1;

另请参阅此帖子和这个

You get this compilation error because compiler doesnt know if ans will ever be initialized,
reason being at the compile time it is not known if the switch condition will ever be executed hence the compilation error. To resolve it initialize ans to some value like :